Department of Clinical Pharmacology and Institute of Pathology and Pathophysiology, China Medical University, No. 92 Beier Road, Heping District, Shenyang, People's Republic of China.
Neurochem Res. 2013 Nov;38(11):2364-74. doi: 10.1007/s11064-013-1149-2. Epub 2013 Sep 14.
Neuronal excitation leads to an increase of the extracellular K(+) concentration ([K(+)]o) in brain. This increase has at least two energy-consuming consequences: (1) a depolarization-mediated change in intracellular pH (pHi) in astrocytes due to depolarization-mediated increased activity of the acid-extruding Na(+)/bicarbonate transporter NBCe1 (driven by secondary active transport, supported by ion gradients established by the Na(+), K(+)-ATPase); and (2) activation of cellular reuptake of K(+) mediated by the Na(+), K(+)-ATPase in both neurons and astrocytes. Astrocytic, but not neuronal increase in NBCe1 activity and pHi is also seen after chronic treatment with either of the two anti-bipolar drugs carbamazepine or valproic acid. The third 'classical' anti-bipolar drug, 'lithium' increases astrocytic pHi by a different mechanism (stimulation of the acid extruding Na(+)/H(+) exchanger NHE1). The acid extruder fluxes, which depend upon the change in pHi per time unit (ΔpHi/Δt) and intracellular buffering power, have not been established in most of these situations. Therefore their stimulatory effects on energy metabolism has not been quantitated. This has been done in the present study in cultured mouse astrocytes. pHi was determined using the fluorescent pH-sensitive indicator BCECF-AM and an Olympus IX71 live cell imaging fluorescence microscope. Molar acid extrusion fluxes (indicating transporter activity) were determined as pHi changes/min during recovery after acid-loading with NH3/NH4 (+), NBCe1 mRNA and protein expression in the cultured cells by, respectively RT-PCR and Western blotting. Drug-induced up-regulation of acid extrusion flux was slow and less than physiologically seen after increase in K(+) concentration. Energetically, K(+) uptake is much costlier than NBCe1 activity.
神经元兴奋导致细胞外钾浓度 ([K(+)]o) 增加。这种增加至少有两个需要能量的后果：(1) 由于去极化介导的 Na(+)/碳酸氢盐转运体 NBCe1 活性增加，导致细胞内 pH 值 (pHi) 去极化介导的变化（由次级主动转运驱动，由 Na(+), K(+)-ATP 酶建立的离子梯度支持）；(2) 神经元和星形胶质细胞中 Na(+), K(+)-ATP 酶介导的细胞内 K(+) 再摄取的激活。慢性使用两种双相抗精神病药卡马西平和丙戊酸后，也观察到星形胶质细胞 NBCe1 活性和 pHi 增加，但神经元没有增加。第三种“经典”双相抗精神病药“锂”通过不同的机制增加星形胶质细胞 pHi（刺激酸外排 Na(+)/H(+) 交换器 NHE1）。酸外排器通量取决于每个时间单位的 pH 值变化 (ΔpHi/Δt) 和细胞内缓冲能力，在大多数情况下尚未确定。因此，它们对能量代谢的刺激作用尚未量化。本研究在培养的小鼠星形胶质细胞中进行了这项工作。使用荧光 pH 敏感指示剂 BCECF-AM 和 Olympus IX71 活细胞成像荧光显微镜测定 pHi。通过 RT-PCR 和 Western blot 分别测定培养细胞中 NH3/NH4 (+) 酸加载后 pHi 变化/min 时的酸外排摩尔通量（指示转运体活性）、NBCe1 mRNA 和蛋白表达。药物诱导的酸外排通量上调缓慢，且低于生理条件下 [K(+)]o 增加时的上调。从能量角度来看，K(+) 摄取比 NBCe1 活性昂贵得多。
